docs: def watermark_process():
      """Apply a watermark to a PDF file."""
      # Redirect to watermark page that contains form
      if not request.method == 'POST':
          abort(403)
  
      # Check if the post request has the file part
      if 'pdf' not in request.files:
          abort(403)
  
      # Retrieve PDF file and parameters
      file = request.files['pdf']
  
      # If user does not select file, browser also submit an empty part without filename
      if file.filename == '':
          abort(403)
  
      # Check if the file is an allowed file type
      if not allowed_file(file.filename):
          abort(403)
  
      params = {
          'address': request.form['address'],
          'town': request.form['town'],
          'state': request.form['state'],
      }
  
      # Save file to uploads folder
      filename = secure_filename(file.filename)
      file_path = os.path.join(app.config['UPLOAD_FOLDER'], filename)
  
      # Make uploads directory if it does not exist
      if not os.path.exists(app.config['UPLOAD_FOLDER']):
          os.mkdir(app.config['UPLOAD_FOLDER'])
  
      file.save(file_path)
  
      # Create new watermarked file and return file path
      watermarked = apply_watermark(file_path, params)
      return send_from_directory(app.config['UPLOAD_FOLDER'], os.path.basename(watermarked))